1. Field of the Invention
The present invention relates generally to increasing the utilization of light emitting diodes (LEDs) mounted on printed circuit boards. More particularly, the present invention relates to allowing multi-stack surface mounted LEDs and decreasing the board space required by the LEDs.
2. Description of the Related Art
In a conventional computer system, printed circuit boards (PCBs) are used to mount semiconductor chips and other electronic components. Computers typically use several types of PCBs including motherboards and various expansion boards. The motherboard usually contains the central processing unit (CPU), memory, and controllers for the computer. Examples of expansion boards include graphics, video, and disk drive cards, as well as local area network (LAN) cards.
An LED is an electronic device that radiates light when electricity is passed through it. LEDs are extremely versatile and thus, widely used in various electronic fields. For example, LEDs are good for displaying images because they can be relatively small, and they do not burn out. With regard to computers, LEDs are mounted on PCBs to function as indicators. For example, an LED mounted on an expansion board may radiate light in different colors to indicate the status of the board. A green light typically indicates a good status, while a red light typically implies that something is wrong.
FIG. 1A is a frontal view and FIG. 1B is a side view of a typical multi-stacked through hole mount (THM) LED module 10 mounted on a PCB 12. LED package 10 includes three LEDs 14, 16, and 18 coupled to a THM housing 20. THM housing 20 is usually mounted about a half a millimeter off PCB 12. Each LED 14, 16, and 18 includes a cathode and anode wire extending outside THM housing 20 for connecting it with PCB 12. Because the wires are bent to allow LEDs 14, 16, and 18 to emit light along the same plane as PCB 12, the LEDs are known as right angle LEDs.
While LED package 10 has generally been an adequate apparatus to house LEDs in computer systems, it has many limitations. As can be seen from FIGS. 1A and 1B, the structure of LED package 10 is not very sturdy. Because PCBs are still often manipulated by hand and because LED package 10 juts out from the surface of PCB 12 when mounted, it is fragile and quite easy to break by accident. THM-LED packages are also frequently broken by test equipment. Furthermore, as computer technology continues to improve, PCBs become more and more densely populated with chips and other components, adding to the difficulty. One form of sturdier LED package that has been developed is known as a surface mount device (SMD) LED package.
FIG. 2A is a top view and FIG. 2B is a back view of a typical SMD-LED package 22. Unlike THM-LED package 10, SMD-LED package 22 is mounted directly onto PCB 24, rising only slightly above the surface of the board. SMD-LED package 22 also includes a LED die 26 encased in a SMD housing 28, which includes a layer of epoxy 30 so that LED die 26 is able to emit light through it. In addition, the bottom of SMD housing 28 is also a form of circuit board material and includes a cathode surface 32, a reinforcing non-electrode pin 34, and an anode surface 36, all of which are soldered to PCB 24. The actual solder material is not illustrated for purposes of clarity in FIG. 2B.
As is shown from FIGS. 2A and 2B, SMD-LED packages have many advantages over traditional THM-LED packages. A SMD-LED package is much sturdier and smaller by comparison. Therefore, in addition to minimizing breakage, SMD-LED packages use much less space, allowing for more efficient utilization of the PCB. Furthermore, SMD-LED packages are much easier to manufacture. Automated machines are able to xe2x80x9cpick and placexe2x80x9d surface mounted devices at phenomenal rates.
However, a major problem with SMD-LED packages is that they are not able to house and utilize multiple LEDs, unlike the THM-LED packages shown in FIGS. 1A and 1B. To display multiple signals, multiple SMD-LED packages must be used instead of a single multi-stacked THM-LED package, requiring far too much valuable space on a PCB. In addition, the inability to use multiple LEDs is a major disadvantage because there are many applications where PCBs need to send multiple signals to transmit information to either a technician or an end user.
In view of the foregoing, it is desirable to have a method and apparatus that provides for a multi-stacked SMD-LED package to reduce the risk of breakage. It is also desirable to have a multi-stacked SMD-LED package to display multiple status signals so that space can be more efficiently used on a PCB.